Thermoelectric elements that use thermoelectric semiconductor elements made of compounds such as bismuth/tellurium compounds, iron/silicon compounds, or cobalt/antimony compounds are used in applications such as cooling/heating devices. Such a thermoelectric element is convenient as a cooling/heating source that does not use liquids or gases, takes up little space, is not subject to rotational friction, and does not require maintenance.
This thermoelectric element generally comprises two types of thermoelectric semiconductor element, p-type and n-type, arranged alternately in an array, with the thermoelectric semiconductor elements being connected to electrodes by soldering to form a ".pi."-shaped series circuit; the thermoelectric semiconductor elements and metal electrodes are sandwiched between ceramic substrates having metal films, and such an assembly is widely used as a thermoelectric module.
The structure of a thermoelectric module that is known in the art is shown in FIGS. 16A and 16B. In this case, FIG. 16A is a front view and FIG. 16B is a perspective view. As shown in these figures, thermoelectric semiconductor elements 63 consisting of n-type and p-type thermoelectric semiconductor elements are arrayed alternately. Upper and lower surfaces of the thermoelectric semiconductor elements 63 are connected with the upper surfaces thereof being connected by metal electrodes 62 and the lower surfaces thereof being connected by metal electrodes 64, so that all of the thermoelectric semiconductor elements 63 are eventually connected electrically in series. The connections between the upper and lower metal electrodes 62 and 64 and the thermoelectric semiconductor elements 63 are performed by soldering. The metal electrodes 62 and 64 at the upper and lower sides are connected onto metallized ceramic substrates 61 and 65, respectively, to fix the entire assembly together. The thus constructed thermoelectric element is usually called a thermoelectric module.
A DC power source is connected to electrodes at each end of this thermoelectric module, and, when a current flows in the direction from each n-type thermoelectric semiconductor element to a p-type thermoelectric semiconductor element, the Peltier effect ensures that the upper portion of the ".pi." shape acts as an absorbing-side cold junction (CJ) and the lower portion thereof acts as a radiating-side hot junction (HJ). Reversing the connection direction of the power source changes the directions in which heat is absorbed and emitted. This phenomenon is utilized so that the thermoelectric element can be used in a cooling/heating device.
Such a thermoelectric module is useful in a wide range of applications, from the cooling of devices such as large-scale integrated circuits (LSIs), computer central processing units (CPUs), and lasers, to use in insulated refrigerators.
If such a thermoelectric module is used as a cooling device, it is necessary to disperse heat efficiently from the heat-radiating side. Methods that are used in the art for dispersing heat from the heat-radiating side of a thermoelectric module include an air-cooling method wherein radiator fins 71 are attached to the heat-radiating side of the thermoelectric module 60 and an air-flow from a fan 72 is directed towards those radiator fins 71, as shown in FIG. 17A, and a liquid-cooling method wherein a liquid-cooling jacket 81 is attached to the heat-radiating side of the thermoelectric module 60 and a coolant passes within this liquid-cooling jacket 81. In addition, a Peltier cooling device is known, which uses aluminum substrates with oxidized surfaces instead of the ceramic surfaces, and which is capable of efficiently cooling the aluminum substrate on the heat-radiating side by using a liquid-cooling jacket provided with injection nozzles. Note that the hollow arrows in FIG. 17A indicate the flow of air and the solid arrows in FIG. 17B indicate the flow of coolant. In both FIGS. 17A and 17B, CL denotes a cooling load.
However, since the thermoelectric semiconductor elements in each of these cooling devices have a structure such that they are cooled indirectly through a ceramic substrate on the lower sides thereof, the heat cannot be dispersed efficiently from the heat-radiating side of the thermoelectric module. In addition, the ceramic substrates 61 and 65 that are fixed above and below the thermoelectric module of FIG. 16A form a rigid structure, so that large thermal stresses are inevitably applied to the thermoelectric semiconductor elements 63 during operation, and thus the lifetime of these thermoelectric semiconductor elements is short.
It is therefore an objective of this invention to provide a thermoelectric element which can minimize any drop in the cooling efficiency is minimized and also extract the maximum from the capabilities of thermoelectric semiconductor elements, by directly cooling the thermoelectric semiconductor elements and metal electrodes on a heat-radiating side thereof.
Another objective of this invention is to provide a thermoelectric element that can have an extended lifetime, by reducing thermal stresses applied to the thermoelectric semiconductor elements.
A further objective of this invention is to provide a thermoelectric cooling or heating device that has a high level of cooling efficiency or heating efficiency, by using this thermoelectric element.
A still further objective of this invention is to provide a thermoelectric cooling or heating device that can keep the temperature of a heat exchange fluid at a constant value, even when it is used over a long period of time or when the ambient temperature changes.